Most Recent Bulletin Report: March 2013 (BGVN 38:03)

This is our first report on Nikko-Shirane (also known as Nikko-Shiranesan). The volcano is located in the Nikko National Park in central Honshu, the main island of Japan (figures 1 and 2).

Figure 1. A photo and a sketch map highlighting the Nikko-Shirane's morphology and location. The volcano sits ~124 km NNW of Tokyo. Courtesy of JMA.

Figure 2. Photo of Nikko-Shirane taken on 8 October 2012 with Goshikinuma Pond in the foreground. Courtesy of futurelight(*busy*) on Flickr.

According to the Japan Meteorological Agency (JMA), after the massive 11 March 2011 MW 9.03 earthquake off the Pacific coast of Tohoku (38.297°N, 142.372°E), seismicity briefly increased 5-10 km E and SE of Nikko-Shirane at a depth of about 5 km W and NW. On 9 April 2011, an M 3.5 earthquake occurred about 5 km W of the summit, followed by several aftershocks. On JMA's earthquake intensity scale, the M 3.5 earthquake ranged from 1 (felt slightly by some people in quiet environments) to 3 (felt by most people in buildings and some people walking; many people awoken). (JMA's earthquake intensity scale is explained on their website.)

In May, two small earthquakes occurred NW of the volcano. Afterward, seismicity gradually declined through December 2011, although several additional small earthquakes through September 2011 were felt in nearby Nikko city, about 4-5 km E of the summit. No volcanic tremor or fumaroles were observed. No changes were also noted during a 2 November 2011 field survey.

The next JMA-translated report on Nikko-Shirane, in February 2013, noted that volcanic seismicity remained low. However, on 25 February an M 6.3 earthquake occurred, the hypocenter of which was 10 km NNE of the summit and 3 km below sea level. The earthquake's maximum seismic intensity on JMA's scale was 5+ in Nikko City (scale of 5 indicates that many people find it hard to move and walking is difficult). Aftershocks with maximum seismic intensities between 1 and 4 on the JMA scale continued until 28 February, when seismicity declined. This seismicity was not accompanied by volcanic tremor, fumarolic activity, crustal deformation, or any other volcanic activity.

Bulletin Reports

All information contained in these reports is preliminary and subject to change.

This is our first report on Nikko-Shirane (also known as Nikko-Shiranesan). The volcano is located in the Nikko National Park in central Honshu, the main island of Japan (figures 1 and 2).

Figure 1. A photo and a sketch map highlighting the Nikko-Shirane's morphology and location. The volcano sits ~124 km NNW of Tokyo. Courtesy of JMA.

Figure 2. Photo of Nikko-Shirane taken on 8 October 2012 with Goshikinuma Pond in the foreground. Courtesy of futurelight(*busy*) on Flickr.

According to the Japan Meteorological Agency (JMA), after the massive 11 March 2011 MW 9.03 earthquake off the Pacific coast of Tohoku (38.297°N, 142.372°E), seismicity briefly increased 5-10 km E and SE of Nikko-Shirane at a depth of about 5 km W and NW. On 9 April 2011, an M 3.5 earthquake occurred about 5 km W of the summit, followed by several aftershocks. On JMA's earthquake intensity scale, the M 3.5 earthquake ranged from 1 (felt slightly by some people in quiet environments) to 3 (felt by most people in buildings and some people walking; many people awoken). (JMA's earthquake intensity scale is explained on their website.)

In May, two small earthquakes occurred NW of the volcano. Afterward, seismicity gradually declined through December 2011, although several additional small earthquakes through September 2011 were felt in nearby Nikko city, about 4-5 km E of the summit. No volcanic tremor or fumaroles were observed. No changes were also noted during a 2 November 2011 field survey.

The next JMA-translated report on Nikko-Shirane, in February 2013, noted that volcanic seismicity remained low. However, on 25 February an M 6.3 earthquake occurred, the hypocenter of which was 10 km NNE of the summit and 3 km below sea level. The earthquake's maximum seismic intensity on JMA's scale was 5+ in Nikko City (scale of 5 indicates that many people find it hard to move and walking is difficult). Aftershocks with maximum seismic intensities between 1 and 4 on the JMA scale continued until 28 February, when seismicity declined. This seismicity was not accompanied by volcanic tremor, fumarolic activity, crustal deformation, or any other volcanic activity.

Nikko-Shiranesan is a relatively small, 2578-m-high andesitic volcano consisting of a group of four lava domes resting on a shield volcano that rises to the NW of scenic Lake Chuzenji in Nikko National Park. All historical eruptions, recorded during the 17th-20th centuries, have consisted of phreatic explosions from Shiranesan, the youngest lava dome. Viscous lava flows with prominent levees from the underlying shield volcano Keizukayama were responsible for the formation of several scenic lakes north of the volcano.

This compilation of synonyms and subsidiary features may not be comprehensive. Features are organized into four major categories: Cones, Craters, Domes, and Thermal Features. Synonyms of features appear indented below the primary name. In some cases additional feature type, elevation, or location details are provided.

Synonyms

Nikko-Sirane | Ara-yama | Nyotai-san | Nikko-Shirane

Cones

Feature Name

Feature Type

Elevation

Latitude

Longitude

Keizuka-yama

Shield volcano

1885 m

Domes

Feature Name

Feature Type

Elevation

Latitude

Longitude

Konsei-zan

Dome

2242 m

Shirane-san
Sirane-san

Dome

2578 m

Zazen-yama

Dome

2320 m

Nikko-Shirane is a relatively small volcano consisting of a group of four lava domes resting on a shield volcano in Nikko National Park. The summit lava dome, cut by an E-W-trending fissure, is seen here from Mae-Shirane, east of the summit. Goshiki-numa forms the depression between Shirane and Mae-Shirane. All historical eruptions, from the 17th-19th centuries, have consisted of phreatic explosions from Shirane-san, the youngest lava dome.

Photo by Lee Siebert, 1964 (Smithsonian Institution).

The following references have all been used during the compilation of data for this volcano, it is not a comprehensive bibliography. Discussion of another volcano or eruption (sometimes far from the one that is the subject of the manuscript) may produce a citation that is not at all apparent from the title.

WOVOdat is a database of volcanic unrest; instrumentally and visually recorded changes in seismicity, ground deformation, gas emission, and other parameters from their normal baselines. It is sponsored by the World Organization of Volcano Observatories (WOVO) and presently hosted at the Earth Observatory of Singapore.

EarthChem develops and maintains databases, software, and services that support the preservation, discovery, access and analysis of geochemical data, and facilitate their integration with the broad array of other available earth science parameters. EarthChem is operated by a joint team of disciplinary scientists, data scientists, data managers and information technology developers who are part of the NSF-funded data facility Integrated Earth Data Applications (IEDA). IEDA is a collaborative effort of EarthChem and the Marine Geoscience Data System (MGDS).